1. Field of the Invention
The present disclosure relates to an apartment-shaped anaerobic digester for producing biogas.
2. Description of the Related Art
Anaerobic digestion, also known as “methane fermentation”, is a biological treatment method for stabilizing organic waste such as food waste, livestock waste, sewage sludge, manure, etc., and a treatment method for hydrolyzing high-molecular organic materials in the presence of facultative and obligate anaerobes under anaerobic conditions, producing volatile fatty acids such as acetic, propionic, butyric acids, etc., and finally gasifying them into methane, hydrogen, carbon dioxide, ammonia, and hydrogen sulfide.
These anaerobic digestions have not been actively used due to widespread adoption of activated sludge methods, but since the mid-1970's oil crisis many studies have been actively conducted on forms of petroleum replacement energy due to their advantages such as availability of recovered gases (CH4 60-70%, CO2 30-40%) for fuel, lower power consumption compared to activated sludge methods that require venting large volumes of air, significantly lower biological sludge generation per unit of organic matter compared to aerobic treatment methods, high value as a fertilizer due to the abundance of nitrogen, phosphorus, humus, etc., in the digested sludge, and an environment-friendly resource renewal method for producing fuel and fertilizer in addition to a simple waste decomposition and treatment function.
An anaerobic digestion process is basically divided into the two steps of acid production and methanogenesis. Because microbes in each step are very different in physiological characteristics and nutritional requirements, a balance between two biological groups is offset to inhibit the efficiency of the overall process when external conditions are changed. As an alternative, a two-step fermentation process (two-phase method), which divides a reactor into two reactors for acid production and methanogenesis steps, was suggested. Because acid production and methanogenesis occur simultaneously in a reactor in the traditional first step reaction process (one-phase method), there are limitations in that it is impossible to optimally control the acid production and methanogenesis steps, and stability is not maintained due to its sensitivity to changes in externally-introduced waste. On the contrary, the two-phase method is advantageous in that environmental conditions suitable for each step may be easily maintained, the loading rate into the methane reactor may be appropriately controlled, and inhibition of methane fermentation may be prevented in advance due to its prevention of rapid pH decrease by accumulation of lower fatty acids. However, these two-phase methods are disadvantageous in terms of costs because reactors must be separately provided, thereby requiring a system for transfer from a first reactor to a second reactor, and are complicated in that reaction conditions in each reactor must be separately controlled.
Thus, the present inventors have conducted studies on a novel one-phase method for performing the acid production and methanogenesis steps in one anaerobic digestion reactor instead of the conventional two-phase methods and improving upon the difficulties in simultaneously satisfying optimal conditions for acid production and methanogenesis, which have been identified as problems in conventional one-phase methods, and have developed an apartment-type anaerobic digester for transferring an inflow such as animal manure or food waste within one anaerobic digestion reactor in a first-in and first-out manner and in which optimal conditions may be appropriately provided according to the process flow, thereby leading to completion of the present invention.